Sorry that this post is not going to be very technical, I just don't know where to start with this, I feel pretty lost. Basically I used to own a nVidia 9600gt which handled Ubuntu just fine on this PC (last tested it with 11.10). However I have since upgraded to an AMD 7750 and am having lots of issues with Ubuntu 12.04 and 12.10.

To start with, if I don't have auto login enabled, lightdm will load and then completely freeze up, even after trying to fix listed in the sticky. Once I got around this issue by having auto login enabled, (lightdm still doesn't work though) I am on Unity 2D with a flickering mouse cursor and no sound.

Now after researching what is going wrong, I found out that my card is not supported by the kernel in 12.04, so I tried to upgrade that to 3.4 which failed miserably, so I installed Ubuntu again from scratch. I then found out that the Catalyst driver 12.4 should add support for my graphics card, however it was extremely buggy, running the screen at the wrong resolution, constantly spewing error messages at me and still having no sound.

To elaborate more on the sound issue, I cannot enter the sound options from the system settings either, it just freezes up the window. These are the two main issues, there is other random quirkiness too, but nothing repeatable or really significant.

I'm not sure what else I can say, I'll give my hardware specs below. I should say that I haven't changed any hardware other than the graphics card since it last worked and that I have a copy of Ubuntu 12.04 on my laptop that works flawlessly, so it is not my copy of Ubuntu either. Anyway, here are my important specs:

It might be important to mention that my motherboard has an onboard nVidia 9200GT graphics chip on it, but I am driving my monitor through the AMD, not the motherboard. Unfortunately I'm not sure how to tell from Windows 7 what the model of motherboard I have is, but the computer is a Packard Bell iMedia if that helps at all.

Thanks for your time.

EDIT: I do still own the 9600gt and I should be able to plop it back into the system if needed.

I've got the exact same problem. Radeon HD 7750 and no login screen (otherwise it'll freeze), no sound (no sound menu at all), default drivers give me that water mark, so I installed the official Catalyst 12.6 driver. Also random freezes. Hope it'll get better in the future, because now it's a pile of sh*t.

Have everything running well after installing the AMD Catalyst 12.8 drivers from the Ubuntu Edgers PPA. Obviously running 12.10 prior to release and installing from the Edgers PPA is not ideal and may lead to other instability in your system, but it will get you up and running with the AMD Readeon HD 7750 card in Ubuntu fairly quickly. Here's a link to instructions. I was not able to install the fglrx-installer package, but installing the fglrx-updates package from this repository included the latest version of the proprietary driver.